Almost a Mile Below South Dakota, A Race to Find Dark Matter

One of the biggest mysteries of physics could end with what scientists find 4,850 feet below the Black Hills of South Dakota

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Between 1876 and 2002, the people of Lead, South Dakota, extracted $3.5 billion worth of gold from the Homestake mine. It was the town’s main business, and when falling prices and diminishing returns finally shut it down, no one was sure what to do with the remaining 8,000-foot hole in the ground. Then, in 2007, the National Science Foundation decided that an 8,000-foot hole would be the perfect place to put its proposed Deep Underground Science and Engineering Laboratory, or DUSEL, a massive research complex that will include the world’s deepest underground lab.

Clean Room:
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Now a team of physicists and former miners has converted Homestake’s shipping warehouse into a new surface-level laboratory at the Sanford Underground Laboratory. They've painted the walls and baseboards white and added yellow floor lines to steer visitors around giant nitrogen tanks, locker-size computers and plastic-shrouded machine parts. Soon they will gather many of these components into the lab’s clean room and combine them into LUX, the Large Underground Xenon dark-matter detector, which they will then lower halfway down the mine, where—if all goes well—it will eventually detect the presence of a few particles of dark matter, the as-yet-undetected invisible substance that may well be what holds the universe together

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The LUX project is just one of at least 10 efforts worldwide to find direct evidence of dark matter, and with a Nobel Prize and longer-term federal investment in play, the 50 researchers of LUX and 2,848 citizens of Lead (pronounced “leed”) are pretty open about wanting to be first. But already there are problems.

For several hours now on this June afternoon, I’ve been watching through a window into the clean room as four physicists dressed in identical white Tyvek suits, latex gloves, blue booties, surgical masks and protective glasses prepare to connect two of the primary components of the detector. The inner cryostat is a hollow cylinder the size of a trash can that everyone refers to simply as “the can,” and at the moment it is down below floor- level in a grate-covered pit. Hanging from a frame above the pit is the dome, which is a kind of lid for the can, and hanging from the dome itself is a complex assemblage called the skeleton. The idea is to carefully raise the can up around the skeleton, nesting one inside the other like a matryoska doll, until it connects with the dome cap, making a perfect seal.

The entire assemblage will eventually contain 31 gallons of –154°F liquid. xenon—the medium that will actually detect the dark matter— so precision is essential. But the various parts were machined at different sites, and without that perfect seal, air and impurities could infiltrate the experiment, potentially compromising the results. As Tom Shutt, a physicist at Case Western Reserve University and the co-founder of the LUX project, explains, “We’ve been on pins and needles to know how tight this can will be.”

No one knows what dark matter is, or if it even really exists. For now, it is just a placeholder, an x that must be plugged into various calculations in order to square astronomical observations with the rules of Newtonian physics. The name comes from Fritz Zwicky, a Swiss astronomer who in 1933 used two well-established methods to calculate the mass of the Coma cluster, a group of more than 1,000 galaxies. One calculation was extrapolated from the movement of eight galaxies in the cluster using Newton’s second law of motion, which says, in essence, that the bigger the galaxy, the faster it spins. The other estimated the cluster’s total mass by quantifying the amount of light given off by its stars.

Source: www.popsci.com...


Well, I won't pretent to indicate I know anything about this...

But I contend they don't either.

Seems like a lot of money being spent trying to prove something they don't even know exist.

So, lets say they determine Dark Matter. I don't really understand the big deal. it's there doing it's thing alreay-regardless if we know it is there or not.

Looking for info/thoughts.

reply to post by anon72


They have to prove it exists because without it, the math of the universe doesn't add up...I think.

I don't know what a big can of xenon is supposed to do or what lowering it in the ground does either.

EDIT - After reading the second page...

Most WIMPS will evade the detection medium, but Shutt and Akerib theorize that around three or four per year will bump into the nucleus of one of the 1.6 octillion (that’s a billion billion billion) xenon atoms in LUX’s tank, and that when one does, it will set off two minuscule flashes of light— the first direct evidence that dark matter exists.

Dark Matter Recipe:

Take equal parts bad math and observational hubris.
Add copious amounts of money and a limited number of observers.

Stir without thinking until better minds and observers provide a better answer.

Originally posted by anon72
Seems like a lot of money being spent trying to prove something they don't even know exist.

So, lets say they determine Dark Matter. I don't really understand the big deal. it's there doing it's thing alreay-regardless if we know it is there or not.

The article says it's one of at least 10 operations like this....some have been running for decades and never found anything, which I don't really understand. If you run the thing for 10 years and find nothing, why run it in year 11, what's going to be different?

And why do we need more of these facilities? can't we just upgrade the ones already in operation? I don't see why we need more than 5 of them. While I think this is important research, it seems like it's being overdone so I agree with you that it seems like a lot of money being spent trying to prove something they don't even know exist. I can see why we might need 5 facilities like this but I don't understand why we need 10 or more.

But the dark matter mystery is one of the great unsolved mysteries of the universe. I wonder if they will find much of it in MACHOs, or Massive Compact Halo Objects, black holes, etc. They have explanations about why MACHOs and black holes can't account for all the missing matter, but I think there are some flawed assumptions in those explanations.

www.labspaces.net...

MACHOs can be any non-luminous stellar object, including black holes, neutron stars and brown dwarfs. White dwarfs and very faint red dwarfs have also been considered, but these are not totally “dark” as they do emit small amounts of light. Because of their mass, MACHOs can be detected using gravitational microlensing – a method that looks at how light coming from a distant star has been bent by the object in question. Using this technique, limits have been set on the mass of individual MACHOs in the galactic halo of our own galaxy, the Milky Way. There are some disagreements between results from different groups (seehere for results from the MACHO project, and here for results from the Eros-2 project). However, overall, it has been found that stellar objects make up no more than a few percent of the mass in our galactic halo.

This means that MACHOs can’t explain the whole dark matter problem.

I have to wonder if the solution to the dark matter problem is that the quoted analysis and conclusion is flawed, and there are problems with the assumptions, computations or conclusions inferred, and that MACHOs explain far more than most people think. And MACHOs can't be detected by these underground mines, they are for detecting the other dark matter candidate:

The most favoured hypothesis when it comes to non-baryonic dark matter, which we know constitutes the lion’s share of dark matter, is that it is made up of particles that were created in the early universe and were stable enough to survive to this day.

That's what the underground mine detectors are for. But I'd like to know how many decades they need to run these detectors with no results before they decide to shut them down, or at least upgrade the detectors? And some of the theories positing these speculative things have been questioned:

Neutrinos are one such particle. ... they can only account for up to 30% of dark matter.

The final candidates are axions...Some experiments are searching for axions, but as yet there is no experimental support for the axion model. It has recently been suggested that since the model may cause a bigger problem than the one it was invented to solve, the model should be scrapped.

So those MACHOs, neutrinos and axions are 3 possibilities but the underground mines are set up to look for a 4th explanation, the WIMPS such as the neutralino, the superpartner of the neutrino.

I guess the burning reason we want to solve the dark matter problem is just to satisfy our curiosity to understand the universe. Our gravity calculations seem to work fine within our own solar system for things like the Pioneer and Voyager missions, with the exception of the Pioneer anomaly which may finally be solved according to a new paper though that explanation is disputed. If that explanation for the Pioneer anomaly is wrong, the anomaly could have something to do with dark matter or dark energy, or some other modification of the natural laws as we know them. But I have to say the effect is so small, it's really splitting hairs.

On a galactic scale, the effect of dark matter, in contrast, is quite large and appears to have a mass from 25% to 100% as large as the mass of the luminous matter. On a larger scale of galaxy clusters the amount of "missing matter" is even larger:

astro.berkeley.edu...

The mass-to-luminosity ratio increases to 300 for groups and clusters of galaxies over a length scale of about 1 megaparsec. Over this scale, 95 percent of the measured mass is dark.

So if most of the universe is missing, aren't you curious about why? That's the big deal, solving that mystery.

reply to post by anon72


They will come up empty.

Dark matter and the associated Dark Energy, are just figments of imagination for those who will not recognize the existance of a multiverse.

It is a simple addition to the law of Gravity to account for this "dark matter", but instead it has spawned a virtual cult, hiding among real scientists, who dare not call it out for funding issues.

Heinlein was right: most so-called scientists are merely button sorters and bottle washers.

Originally posted by mydarkpassenger
Dark matter and the associated Dark Energy, are just figments of imagination for those who will not recognize the existance of a multiverse.

Dark matter and energy are admittedly "placeholders" and aren't claimed to be anything but that.

But if a multiverse theory is proven to explain observations, why wouldn't scientists accept it? It seems the only thing lacking is proof. And if there's no proof, why should they accept it as the explanation for dark matter? The best you can do is list multiverse theory to a long list of possible suspects and investigate all of them until you have proof of the correct answer.

reply to post by Arbitrageur


In my opinion, science is all about observations/calculations leading to a reasonable hypothesis. This hypothesis is then subject to as much scrutiny as possible and, if it stands up, may be sound enough to be accepted as theory. If a theory is able to stand up to all scrutiny against it and pass with flying colours, it may be accepted as a "Law".

Dark Matter isn't doing so well. It seems that many scientists are so desperate to find evidence of this stuff that they ignore all null results and look for other more exotic ways to find it. That's not science. I suspect you agree. If only the Aether had the luxury of so many appeals.......

Perhaps gravity is not so much a "pull" by massive objects but a "push" by so called empty space (of course empty space is far from empty). This might be analogous to the Casimir Effect. Perhaps a hypothesis such as this could offer an alternative to Dark Matter.

Originally posted by OZtracized
In my opinion, science is all about observations/calculations leading to a reasonable hypothesis. This hypothesis is then subject to as much scrutiny as possible and, if it stands up, may be sound enough to be accepted as theory.

They have the observations, and they have enough hypotheses.

What they are lacking is any proof that any of these hypotheses are correct.

So then you have to go back and question both the original observations and related assumptions, and the hypotheses. For example, the assumption that dark matter can't be baryonic seems to reply on inferences from Jupiter's atmosphere:

astro.berkeley.edu...

To estimate how much deuterium was created in the big bang, one has to factor in all the deuterium that has since been destroyed. The percentage of the isotope destroyed since the big bang can be calculated if one knows the its rate of destruction, which can be found by comparing the abundance of deuterated molecules in the atmosphere of Jupiter with the abundance of deuterium in interstellar clouds. One has to choose a value for the density of baryons that cannot exceed about a tenth of the critical density for closure of the universe, or too little primordial deuterium would have been synthesized. Conversely, the density of baryons cannot be too low, below 2 or 3 percent of the critical density, or else one would overproduce deuterium, compared to what is observed in the solar system. If the universe is at critical density, 90 percent of the matter in the universe must be nonbaryonic.

So my question is, if we lived in another solar system and the gas giant there had a different atmospheric composition than Jupiter, we'd come up with a different result, right? So how representative is Jupiter? I'm not comfortable all the assumptions that are made are necessarily correct assumptions, especially the assumptions that rule out baryonic matter as an explanation for dark matter, especially on the galactic scale.

That assumption about Jupiter is just one example, I could go on about the distribution of MACHOs and assumptions about what microlensing effects would be observed, etc. In fact some researchers think that MACHOs explain the dark matter observed on a galactic scale:

Australian and US researchers have found objects, lying in a 'halo' around our galaxy, that could account for about 50 per cent of our galaxy's unseen mass.

The hypothetical star-sized lumps were christened MACHOs - MAssive Compact Halo Objects.

That explains 50 percent of the galaxy's dark matter, but I think they've just scratched the surface on the MACHO microlensing research, so I'm not totally convinced underground mines are needed to detect the other 50%, though I can't rule it out either. I think we have to look in underground mines, but it seems like we're overdoing it. How many people need to sit around in how many underground mines for decades finding....nothing? Isn't that boring?